Lightning-rod



. 0 C S E R P LIGHTNING ROD.

No. 303,591. Patented Aug. 12 1884.

Wavy turf Mao/(W ,2 Sheets-Sheet 2.

(No Model.) 1

G. S.PRESGOTT.

LIGHTNING ROD.

Patented Aug; '12, "1884.

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N. PETERS, PhnloLAlhnpzmphcr. wnsmn mn, D. c.

UNITE STATEs PATENT EETEE.

GEORGE S. PRESCOTT, OF MERRIMAO, ASSIGNOIt. OF ONF-IIALF TO El)\VlNPRESCOTT, OF ARLINGTON, MASSACHUSETTS.

L|GHTNlNG-ROD.

v SPECIFICATION forming part of Letters Patent No. 303,591, dated August12, 1884.-

Application filed May Ill, 1883.

To all whom, it may concern:

Be it known that l, GEORGE S. PnEsco'r'r, of Merrimac, county of Essex,State of Massachusetts, have invented an Improvement in Protectionagainst Lightning, of which the following description, in connectionwith the accompanying drawings, is a specification, like letters on thedrawings representing like parts.

My invention, relating to an improvement in the means employed forprotecting buildings from lightning, is based on facts that have beenobserved by me during a long period of time. It has been stated as a lawby other z -,,observers that lightning strikes or seeks the bed of moistearth or water below the dry surface soil, and that the lightningfollows some definite path which affords the best conductor between thewater-bed of the earth and the storm-cloud, although, so far as I amaware, no law has yet been announced for determining such path, I havediscovered that there are definite places where the lightning willstrike or enter he earth, it never striking at any other point in thevicinity, and I have found that such strikingpoints lie over theundergrou,nd streams of water flowing through fissures or perviousstrata, and distinct from the general bed of water below, thelightning'beo ing especially likely to strike where two or more suchunderground streams cross one another. This law is confirmed by numerousfacts, as follows Buildings provided with lightning-rods have beenstruck, and although 3 5 the conductor had a \vellgroundedearth-terminal, the lightning has left the conductor and passed throughthe building to reach the point which may, for convenience, be calledthe nat ural grounding or striking point. The same 0 building hasafterwards had the rods changed to enter the earth at the point wherethe light ning had previously entered, and the building been againstruck, when the rod conducted the lightning to earth without injury tothe 5 buildin The lightning has in no case left rods which have beengrounded at a point where lightning had previously struck. The abovefacts indicate and long experience has shown that no matter howperfectly a lighthing-rod is grounded the building is nevertheless notprotected if it is located at or near a (No model.)

natural grounding-point which the conductor fails to reach, and,furthermore, the mere increase in the area of groumhcontaet of theearth-terminal of the lightning-rod, if it does not reach nor extendtoward such natural grounding-point, is of no avail. To affordprotection the conductor must reach the natural grounding point, or mustapproach more nearly to it than any part of the building to beprotected, because if there is a good metallic conductor to thegrounding-point the lightning will follow it, rather than break throughthe less conductive material. of the building; but if the good conductorfails to 6 reach such point the lightning will leave it and traverse theinferior conductor to reach the said point, as it must arrive there bysome path. WVhen it is possible to discover the natural grounding-pointin the neighborhood of a building. the building may be perfectlyprotected by a suitable lightning conductor or rod entering the earth atthat point, as the lightning will follow such conductor rather than theless conductive material of the build- 75 ing. It is not, however,always easy nor even possible to discover where such grounding; pointsexist, and the points, if found, might subsequently shift or vary, justas other changes take place in the topography of a 10- So cality.

The present invention has for its object to obviate the necessity ofdiscovering the natural grounding-point, if any exist, and it consistsin providing a metallic conductor arranged to 8 5 connect with allpoints in the neighborhood of the building; or, in other words, providedwith an earth-terminal extending around the building, so that it willreach any natural grounding-point which may exist in the neigho borhoodof the building, or may approach more nearly to such point than any partof the build ing itself. This is accomplished by connecting the usuallightningrods, descending from the roof or top of the building to theground, 9 5 with a metallic conductor extending around or nearly aroundthe base of the building, and connected with the said verticalconductors or lightning rods at or near their lower extremities. Thehorizontal or connecting conductors 10:) or earth-terminals serve toconnect the vertical conductors with the point or places in the earth inthe neighborhood of the buildings that are best adapted to conduct thecurrents or discharges of electricity, and the building is thusperfectly protected therefrom.

Figure 1. shows in perspective view a build-- ing provided with means toprotect it against lightning, in accordance with this invention, andFig. 2 a plan view illustrating the operation.

The building is provided with one or more of the usual verticalconductors or lightningrods, (1, having the proper tips orair-tern'iinals, 0/, extended upward i'roni the roof or chimneys in theusual manner, and passing down the walls of the building toward theground. The said conductors a are connected at or near their lowerextremities with a substantially horizontal eonneeting-conductor orearth-terminal, I), surrounding or nearly surrounding the base of thebuilding. In case the vertical conductors a, distributed in the usualmanner, do not enter the ground at a natural grounding-point near thebuilding, the surrouiuling conductor or earth-terminal I) will form acontinuation of the said vertical eoni'luctors, leading to the bestpoint in the neighborhood o'lthe building for conducting the electricalcurrents away from the said building.

\Vhile the conductors a are spoken of as ver tieal coluluctors, and theearth-terminal I) as a horizontal conductor, it is of course not essential that the said conductors should be exactly vertical orhorizontal, although this will generally be nearly their position withrelation to one another.

in the diagram, Fig. 2 c 0 represent two 'uiulergroiuul streams, thedirections of which cross, producing a natural grounding-point, G,beneath the building, which is thus very dangerously situated. The areasinclosed by the dotted lines d represent very large eartheonneetions oi'the kind commonly employed for the conductors a; but, in spite of suchgreat area of earth-connection, the lightning would be likely to leavethe conductor a and break through the building, as indicated by thedotted arrow 0, to the point G, as this will be the most direct path tothe said point. \Vheu, however, a metallic earth-terminal, b, is used,extending around the building, the lightning will follow the pathindicated by the arrows f from the conductor a along the conductor 1) tothe stream 0, as this path is nearly as dirert as that through thebuilding, and is a far bet ter conductor.

It will be seen that, in order to afford equal protection without themetallic ground-terminal 1) extending from one to another of thevertical conductors around the base 01' the building, it would benecessary to place the vertical conductors so close together that theirgrouiul-eonnection would be practically continuous around the building;but such increased number of vertical conductors would be many timesmore expensive than a hori zontal earth-terminal extending from one toanother of the vertical eomluctors, and .l'orming a continuousearth-terminal leading to every point around the building.

The combination, with a building, of a vertical conductor a, extending.ll'Olll the top of the building to the ground, and an earllr terminal,I), consistiugof a metallic conductor connected with the said verticalconductor and extended around the base of the building, substantially asand for the purpose dcsmiibed.

In testimony whereof I have signed my name to this specification in thepresence oi two sub scribing witnesses.

GEOhGlil S. llllESUOlTT.

Vitnesses:

FRANK. 0. income, 1t. 1t. ScnINsoN.

